Liquid crystal displays (LCDs) are optical displays used in devices such as laptop computers, hand-held calculators, digital watches and televisions. Some LCDs, for example LCD monitors and LCD televisions (LCD-TVs), are directly illuminated using a number of light sources positioned directly behind the LCD panel. This arrangement, commonly referred to as a direct-lit display, is increasingly common with larger displays. One reason for this is that the light power requirements to achieve a certain level of display brightness increase with the square of the display size. On the other hand, the available real estate for locating light sources along the side of the display only increases linearly with display size. Therefore, there comes a point where the light sources have to be placed behind the panel rather than to the side in order to achieve a certain level of brightness. Since some LCD applications, such as LCD-TVs, require that the display be bright enough to be viewed from a greater distance than other applications, and the viewing angle requirements for LCD-TVs can be wider than those for LCD monitors and hand-held devices, it is more common to see LCD-TVs with direct-lit illumination even for relatively small screen size.
Some LCD monitors and most LCD-TVs are illuminated from behind by a number of cold cathode fluorescent lamps (CCFLs). These light sources are linear and stretch across the full width of the display, with the result that the back of the display is illuminated by a series of bright stripes separated by darker regions. Such an illumination profile is not desirable, and so a diffuser plate is commonly used to smooth the illumination profile at the back of the LCD device.
Currently, LCD-TV diffuser plates employ a polymeric matrix of polymethyl methacrylate (PMMA) with a variety of dispersed phases that include glass, polystyrene beads, and CaCO3 particles. These plates often deform or warp after exposure to the elevated temperatures of the lamps. In addition, some diffusion plates are provided with a diffusion characteristic that varies spatially across its width, in an attempt to make the illumination profile at the back of the LCD panel more uniform. Such non-uniform diffusers are sometimes referred to as printed pattern diffusers. They are expensive to manufacture, and increase manufacturing costs, since the diffusing pattern must be registered to the illumination source at the time of assembly. In addition, the diffusion plates require customized extrusion compounding to distribute the diffusing particles uniformly throughout the polymer matrix, which further increases costs.